The present invention relates generally to improvements in a method and apparatus for locating the center of an incident beam on a receiving structure and, more particularly, pertains to a new and improved method and apparatus for locating the center of an incident beam on a receiving array of antenna elements wherein the incident beam is in the microwave region and utilized for the wireless transmission of power.
The concept of transmitting significant quantities of power by way of microwaves differs from the ordinary concept of communications by way of microwaves in that the elements of the microwave power transmission system are designed so that the largest proportion possible of the transmitted beam is intercepted by the receiving part of the system. This is important because in a microwave power transmission system the received power must be a significant portion of the transmitter output. This is not true in a communication system where the received power is typically on the order of hundreds of decibels below the transmitter output. For the purpose of example only, it will be assumed that the base band power output at the receiving end of a power transmission system is in DC. It should be understood, however, the power output may take other forms such as pulsating DC or even low frequency AC in the 60 cycle per second range.
The microwave power transmission system illustrated schematically in FIG. 1 is made up of a high power RF illuminator which is mounted in a well known manner on a tower or a similar mounting device which provides for the pointing of the illuminator in azimuth and elevation. The illuminator is beamed as closely as possible directly at the receiving element of the power transmission system.
The present invention provides a method and apparatus for determining where the center of the beam incident on the receiving structure is located on that structure. For maximum efficiency and power transfer between the illuminator and the receiver, the center of the incident beam should be lined up with the physical center of the receiver array.
Prior art systems that have been concerned with the reception of incident waves at the center of a receiving target have all been concerned with or directed to monopulse radar systems. These monopulse radar systems basically involve a 4 segment receiver element which may take the form of 4 feed horns or multiple dipole elements divided into 4 equal segments. The basic concept involved is that when the receiving array is on target, that is, lined up with the direction from which the reflected signal is being received, all four segments of the receiving array are evenly illuminated as indicated by the sum and difference levels from each of the receiving segments. In addition, these sum and difference levels from each of the feed horns or 4 segments can be used and are used to generate error magnitude signals for re-directing the receiving antenna to receive equal energy at all four segments.
The receiving array of the present invention as shown in FIG. 2 is made up of a plurality of subarrays arranged about a horizontal and a vertical center. This arrangement permits the determination of where the center of the incident beam is located on the receiving array. The monopulse radar technique only provides a general indication of whether the incident beam center is aligned or not aligned with the receiving array.